The present invention relates to a hydrogen separator and a method of operating a hydrogen separator. More particularly, the present invention relates to a hydrogen separator that exhibits excellent hydrogen permeability and durability and suppresses defects of a selective hydrogen permeable metal membrane due to adhesion of an iron-containing substance, and a method of operating the same.
Hydrogen gas has been widely used as a basic material gas in the petrochemical industry, and has also attracted attention as a clean energy source. High-purity hydrogen gas is obtained by selectively separating hydrogen gas from a hydrogen-containing gas produced by various means using a natural gas, naphtha, coal, or a hydrocarbon as a raw material (raw material fluid).
A method that utilizes a hydrogen separator has been known as a means of separating a hydrogen gas. For example, a method that utilizes a hydrogen separator that includes a selective hydrogen permeable membrane that is provided on at least one side of an inorganic porous support and selectively allows hydrogen gas to pass through (selective permeability) has been known.
For example, a selective hydrogen permeable metal membrane represented by a metal film such as a palladium film or a palladium alloy film has been known as the selective hydrogen permeable membrane. The selective hydrogen permeable metal membrane utilizes a phenomenon in which palladium or a palladium alloy dissolves only hydrogen.
A hydrogen separator including the selective hydrogen permeable metal membrane is normally operated in a severe environment (e.g., high pressure, high temperature, or a repeated change in temperature) while repeating a hydrogen separation process. Therefore, a metal member has been used as a member that forms the hydrogen separator in order to improve durability, thermal conductivity, and sealing capability. However, a related-art hydrogen separator has a problem in which defects of a selective hydrogen permeable metal membrane occur, or a decrease in hydrogen separation performance occurs.
Therefore, technology that improves the performance of the selective hydrogen permeable metal membrane of a hydrogen separator has been studied.
For example, JP-A-8-257376 discloses technology that subjects the selective hydrogen permeable metal membrane to a heat treatment in an oxygen-containing gas in order to recover and stabilize the hydrogen permeability of the selective hydrogen permeable metal membrane. According to this technology, carbon or a carbon-containing compound that adheres to the selective hydrogen permeable metal membrane can be gasified and removed by a reaction with oxygen.
According to the technology disclosed in JP-A-8-257376, since carbon or the carbon-containing compound that adheres to the selective hydrogen permeable metal membrane can be removed by repeating a heat treatment in an oxygen-containing gas at intervals between the hydrogen separation processes, the hydrogen separation performance is recovered after the heat treatment in the oxygen-containing gas.
JP-A-2006-289345, JP-A-11-114388, and JP-A-2004-271525 disclose technology that covers the surface of the selective hydrogen permeable metal membrane with a protective layer. A situation in which a substance that floats in the passage of the hydrogen separator directly comes in contact with the selective hydrogen permeable metal membrane is prevented by the protective layer so that the durability of the selective hydrogen permeable metal membrane is improved.
According to the above technology, the substance that floats in the passage can be removed by additionally disposing a filter that contains a ceramic and/or a metal as the main component around the selective hydrogen permeable metal membrane so that contact of the substance with the selective hydrogen permeable metal membrane can be prevented.
However, since a hydrogen separator is normally used at a temperature of 400° C. or more, defects of the selective hydrogen permeable metal membrane and a decrease in hydrogen separation performance are not necessarily prevented even when using the technologies disclosed in JP-A-8-257376, JP-A-2006-289345, JP-A-11-114388, and JP-A-2004-271525.
For example, the technology disclosed in JP-A-8-257376 carries out the heat treatment in an oxygen-containing gas. Therefore, when a member that forms a passage of the raw material gas (raw material fluid) or a member disposed in the passage is made of a metal (e.g., stainless steel), the surface of the metal member is corroded due to oxidation and reduction. Moreover, a material that can be suitably used for the member that forms the passage of the hydrogen separator instead of stainless steel has not been proposed.
According to the technology disclosed in JP-A-2006-289345, JP-A-11-114388, and JP-A-2004-271525, a situation in which the substance that floats in the passage of the hydrogen separator comes in contact with the selective hydrogen permeable metal membrane can be prevented. However, defects of the selective hydrogen permeable metal membrane and a decrease in hydrogen separation performance cannot be reliably prevented. Moreover, since the surface of the selective hydrogen permeable metal membrane is covered with the protective layer, a decrease in productivity and an increase in maintenance work occur.
According to the above technology, a situation in which the substance that floats in the passage comes in contact with the selective hydrogen permeable metal membrane can be prevented by disposing the filter. However, a decrease in productivity and an increase in maintenance work inevitably occur as a result of additionally disposing the filter.